The invention relates to an injection pump for generating high fuel pressure in fuel injection systems of internal combustion engines, having a pump piston, which can reciprocate in a cylinder having a control bore in order to aspirate fuel from a suction chamber into a high-pressure chamber and act upon the fuel with high pressure. A supply onset of the injection pump is defined by when an upper control edge, which is embodied on the pump piston and is oriented toward the high-pressure chamber passes the control bore, and the end of supply by the injection pump is defined by when a lower control edge, which is embodied on the pump piston and is remote from the high-pressure chamber, passes the control bore.
In conventional in-line injection pumps, the supply onset is defined by the closure of the control bore by the piston control edge located at the top. If the piston control edge is embodied obliquely and located at the top, the supply onset can be defined by rotating the pump piston as a function of a motion of a control rod. In this so-called load-dependent injection adjustment, the control path for the injection quantity and the supply onset is fixedly assigned. It is known that a shift in the injection onset closer to top dead center of the engine piston brings about a marked reduction in NOx emissions. However, this also causes a slight increase in fuel consumption.
An object of the invention is to furnish an injection pump in which the supply onset can be set freely for two different operating modes of the engine.
This object is attained in an injection pump for generating high fuel pressure in fuel injection systems of internal combustion engines. The system includes a pump piston, which can reciprocate in a cylinder having a control bore in order to aspirate fuel from a suction chamber into a high-pressure chamber and act upon the fuel with high pressure. A supply onset of the injection pump is defined by when an upper control edge, which is embodied on the pump piston and is oriented toward the high-pressure chamber passes the control bore and the end of supply by the injection pump is defined by when a lower control edge, which is embodied on the pump piston and is remote from the high-pressure chamber, passes the control bore. The cylinder has a second control bore, which cooperates with a plunge cut in the cylinder and with a piston stop groove that extends longitudinally along the pump piston from the upper control edge. The end of supply by the injection pump is always controlled by the lower control edge. By means of the second control bore, a second supply onset is made possible. Once the upper control edge has closed off the associated control bore, the fuel positively displaced by the pump piston can still flow out through the second control bore until such time as the end of the piston stop groove has moved past the top edge of the cylinder plunge cut.
A particular embodiment of the invention is characterized in that the two control bores can be made to communicate in the cylinder with one another and with the suction chamber via a 3/2-way valve. With the 3/2-way valve, a switchover from the first supply onset to the second supply onset can be made. This expands the optimal operating range of the engine. Via a governor, automatic switching from the xe2x80x9ceconomyxe2x80x9d operating mode to the xe2x80x9clow NOx emissionsxe2x80x9d operating mode is possible.
A further particular embodiment of the invention is characterized in that the lower control edge is embodied obliquely. The oblique embodiment of the lower control edge that defines the end of supply offers the advantage, over a control edge extending perpendicular to the longitudinal axis of the piston, that by means of a defined rotation of the pump piston, the same useful stroke can nevertheless be attained despite a different supply onset.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawing. The characteristics recited in the claims and in the description can each be essential to the invention individually or in arbitrary combination.